The motorized window shade mechanism disclosed in U.S. Pat. No. 6,186,211 was a major improvement over other mechanisms of this type known at that time. For example, it was highly effective in reducing the number of components required, increasing reliability, and meeting the rigid requirements associated with use aboard aircraft.
Despite its many advantages, some room exists for attaining further improvements in this product. For example, the aircraft window has a porthole through which light enters the cabin. In addition to the window shade being movable up and down by a drive assembly to control the amount of light being blocked, its width is sized to be wider than that of the porthole by a certain lateral spacing so that the side edge of the window shade extends laterally past the porthole in order to block incoming light. If the lateral extension of the window shade beyond the porthole is small, some light will bleed around the side of the window shade. Thus, it is desirable to make the window shade as wide as possible relative to the porthole. However, since the width of the shell (Wshell) for the window assembly is a given dimension for each aircraft, the width of the window shade (Wshade) is limited by the width of the vertical drive channel (Wdc) through which the drive assembly moves (Wshade=Wshell−2Wdc). The wider is this drive channel, the narrower must be the window shade. Thus, one area for potential improvement is to make this drive channel of motorized window shade mechanism as disclosed in U.S. Pat. No. 6,186,211 narrower.
One embodiment disclosed in U.S. Pat. No. 6,186,211 has two window shades that can be selectively moved into position to block light. One window shade can be translucent while the other is opaque. Each shade has its own motorized drive mechanism. Both motorized drive mechanisms must fit within the small confines of an aircraft window. To accomplish this, the motorized window shade mechanisms as disclosed in U.S. Pat. No. 6,186,211 had the motors inserted in the rail attached to the bottom edge of the shade. Since the motors moved along with the rail as the shade was extended and compressed, a flexible conductive ribbon functioning as a power cable and moving with the motors was required to energize the motors. This cable required its own space in the drive channel within which to travel with the motors. It is desirable to eliminate the need for this cable and for the space it requires. In fact, this is one way for making the drive channel narrower. Also, installing the motors in the rail imposes severe size limitations on the motor, which makes it more difficult to find a suitable motor in terms of size, performance and price. Such an arrangement also makes the rail large, thereby increasing the stack height of the shade assembly, which is undesirable.
Furthermore, motorized window shades can experience motion even though they should be stationary while the drive motor is inactive, i.e. uncommanded motion. Such uncommanded motion can occur due to such factors as the weight of the shade and/or the compression pressure of the shade while the motor is deactivated. It is desirable to eliminate such uncommanded motion.